Amplification system



ID@ 4, v192s. 1,693,898

, L. c. F. HORLE AMPLIFICATION SYSTEM Filed Jan. 24, 1925 2 Sheets-Sheetl O .face/nf Carrer# Guijo/'n3 76 5e Anf/:fied mf//f/ed C u rre n fs gnum 1 fof,

Dec. 4, 1928.

AMPLIFICATION SYSTEM Filed Jan. 24, 1923 2 Sheets-Sheet 2 WAVE LENGTH INMETERS.

x Tozum Patented Dec. 4, 1928.

UNITEDsTATi-:s

PATENT OFFICE.

LAWRENCE C. F. HORLE, OF NEWARK. NEW JERSEY, ASSIGNOR TO FEDERAL TELE-PHONE MANUFACTURING CORFORATION, OF BUFFALO, NEW YORK, A CORPORA- TIONOF NEW YORK. x.

AMPLIFICATION SYSTEM.

Application led January 24, 192t3 Serial No. 614,608.

My invention relates broadly to the amplification of feeble electriccurrents, and more particularly to means `for cgupling the input andoutput circuits of amplifiers operatingA over broad bands of alternatingcurrent frequencies.

One of the objects of my invention is to provide means for coupling aplurality of electric circuits for particular' kinds of current Whileisolating the circuits from one another for other types of currents.

Another object of the invention is to provide 'a means forinterconnecting electricalk circuits which are to be coupled foralternating current and are to be insulated from one another for 'directcurrents or for interconnecting such circuits which are to be coupledfor a band of alternating current frequencies and to be substantiallyinsulated from one another for all other bands of frequencies.

Another object of the invention is to provide a transformer for couplingthe input and output circuits of an electron tube amplifier, thecoupling means being designed to secure substantially pure magneticcoupling with substantially no capacity coupling.

A still further object of the invention is to provide a type of duplexwinding for the circuits of the coupling device and the amplifyingmeans. I X

Another object of the invention is to provide a simplified constructionof coupling device whichl may be manufactured in quantity productionwhere the characteristics of the coupling device must not vary betweenspecimens manufactured under similar conditions and with materials whichvary no more than do the materialsthatare commonly available for theirfabrication.

My invention will be more clearly understood from the followingspecification by reference to the accompanying drawings in which: i

Figure 1 is a wiring diagram of an electron tube amplification circuitemploying my invention; Fig. 2 is a view of an air core transformeremploying the duplex winding of my invention; Fig. 3 is a view of aclosed core transformer employing the duplex winding of my invention;Fig. 4 is a view of an iron core transformer withv primary and secondarywindings in duplex arrangement in accordance with my invention; Fig. 5is a view partially broken away showing the transformer mounted within'an insulated cylindrical casing with terminals for the Windings broughtout at opposite ends of the case; and Fig. (i is a Curve sheet showingthe characteristics of the transformer of my'invention compared with thecharacteristics of transformers heretofore available in the art. I

My invention finds application in such laboratory apparatus as bridgesfor radio frequency use, coupling systems for duplex telephony and forintertube couplings for electron tube amplifiers.

Heretofore in the art several types of radio frequency transformers forcoupling the circuits of an electron tube amplifier/have been employed,including the multilayerv open core transformer in which the windingsare wound adjacent each other in grooves in a form of insulatingmaterial; the iron core multilayer transformer in which the windingsare` mounted inside a closed iron core; the single layer air coretransformer with windings arranged along the periphery of an insulatedtubular member; and the single layer closed iron core transformer.. Thecharacteristics of each of these prior types of transformers have beenrepresented by curves A, B, C and D, respectively, in Fig. 6. i It willbe observed that in every case shown in` the drawings the range overwhich amplification can be accomplished is very narrow and that thedegree of amplification varies rapidly with wavelength. rflhis isseriously objectionable since it means that in the use of apparatus inwhich these transformers are included every minute change of Wavelengthmust vbe accompanied by readjustments of other. controls to maintain theamplifier at its liest amplification and make the operation of theequipment both `cumbersome and relos l in Fig. 6. My transformerconsists of tivo windings, a primary Winding and a secondary winding,the conductors of which are laid on the winding from parallel andseparated from one another only by the thickness of the insulatingmaterial on the conductors. It Will be observed in Fig. 6 that only onewavelength band occiiis in this transformer and that the amplificationchanges only vary slouly with frequency change. The actual amplificationat any Wavelength throughout this band is considerably in excess of theother transformers and because of its change, the stability of operationis very great.

Referring particularly to Fig. l of the drawings, a representativeelectron tube ainplification circuit is shown consisting of means forapplying the incoming poiver which is to be amplified to the vacuum tube3 which in this case is the transfornier l; the vacuum tube 3; thedevice for interconnecting the vacuum tube 3 with the vacuum tube elwhich in this case is the transformer of my invention 2; and the means 6for applying to the system to which the amplifier is connected the powermade available by the amplifier unit. ln addition to these essentialelements there are the batteries A for supplying rthe filaments, and thebatteries B for supplying the exciting current of the tube.

rlhe transformers 1 and 2 are of such a nature that they mostefficiently accommodate the tubes to the incoming and outgoing lines andwill therefore depend in their characteristics upon the nature of thelines. The transformer 2 however must accommodate the outputcharacteristics of the tube 3 to the input characteristics of the tube4, and it must be so designed that any Wave form which eX- ists in thegrid circuit of tube 3 Will be repro- -duced very faithfully in theplate circuit of tubefl, and this must be done With the very maximumgain of energy in the transfer.

Where such an amplifier is devised for amplifying cui-lents of W`frequency-200 to 2000 cycles-as in telephony, it is quite easilypossible to build a transformer which will approximate the idealcharacteristics described above; namely, high efficiency andfaithfulnessfof reproduction by the use of the commonly availablematerials of the telephone art and With the commonly used telephonetransformer design methods. But `here such an amplifier is to be usedfor the aniplification of exceedingly high frequency eurrents-500,000 to5,000,000 cycles-the difficulty of obtaining high efficiency ismultiplied many fold and the difficulty of securing faithfulness ofreproduction overa Wide band gt' frequencies becomes almost insurmounta-Fortunately for the art, however, Where such amplifiers are used for theamplification of high frequencies, as in a radio telephony and similarWork, the same broad freabsolute equality of amplification is not ob-.

tained the quality of the sounds as they are reproduced by devices, suchas telephones or loud speakers, supplied by the amplifier depart greatlyfrom the quality of the sound which is applied to the system of Whichthe amplifier is a part and the amplifier is said to be one of loWquality. But since the characteristics of the Vacuum tubes that areavail-v able are such that the characteristics are practic-ally the sameover this band of frequencies, the problem of building such an amplifierreduces itself to the design of a transformer which has the desirableand constant characteristics over this band of frequencies. And sincethe action of the materials common to the telephone art are reasonablyindependent of frequency this problem has been solved, as have othertransformer problems of the telephone art.

Its best solution is accomplished through the recognition of the factthat the most efficient and satisfactory amplifier is that one whichwill make the greatest voltage available to the grid of electron tube lfor a given voltage available in the plate circuit of tube 3. rllhe onlylimiting condition which is set for making the ratio of the highestpossible value at voice frequencies is the fact that both the platecircuit of tube 3 and the grid circuit of tube 4 are essentiallyresistances and are independent in their values of the frequencies.There are certain capacities existent in these circuits of the tube, andsince the impedance of any capacity depends upon the frequency thecapacity impedances of the tube depend upon the frequency and might beeX- pected to cause the action of the amplifier to vary with frequency.The impedances which result from these capacities, however, are

vfound to be so extremely high at. the frequencies which are used forthis type of aniplification that when compared with the resistances ofthe tube circuits they influence the operation of the amplifier in onlya very minor Way, and if proper provision is made for their use they maybe made to correctJ a contrary variation of the other characteristics ofthe tube circuits.

When the frequencies to be amplified are exceedingly high, however, theimpedances of the tube become predominantly those of the associatedcapacities and the problem of imitiozr Thus, While it is quite common.practice to secure amplification of voice fre quency currents between200 and 2000 cycles-d range of ten to one-it is a more diiicultuniformity of amplification can he ac.- `)lished het-Ween 500,000and'5,000,000 cy- -a range of only two to one. ln the am cation of radiofrequency currents suoli i used in radio telephony, howeverj the overwh" i. uniform amplification must be accomplished in order 'thatfaithfulness oi @duction may be assured may' he rei-y 'When reception ofbroadcastsignals o be done Witi' the amplifier, for instance.5 iormityampi .cation can be gotten a of frequencies of' 1 .2 to l, satisryquality of reproduction he oli ed. fiat Where such an amplifier is to hefr 'for stations operating on Widely difierser# wavelengths must becapable of about saine degree oi: amplification on these severalwavelengths. In order that a radio freciuency amplifier be absolutelyuniversal in its application to radio reception it would be requiredthat it permit amplification on all wavelengths between 200 meters and20,000 meters-1,500,000 and 15,000 cycles. This is practicallyimpossible of accomplishmentJ and t-liefart has had to make useofdevices Whose characteristics depart very greatly from these idealconditions. Heretofore radio frequency amplifiers have been greatlylimited in range, but because of the fact that no amplifier insta-llation is required in actual practice to be used for the manydifferent t pes of radio servlce, which are represente by the very Wideband of wavelengths, the comparatively narrow band amplifier has found avery important place in the field of radio. f

The radio frequency amplifier commonly used also suffers greatly frominstability, a condition that either makes it inoperative at somefrequencies or makes it necessary that it frequency at which it is used.That is, Whenever the frequency at which it is used is changed itusually requires a change in the constants of the associated ap ratusand thereby makes itsuse rather cum rsome and not easily accomplished.

In addition to the abode objections to the forms of radio frequencyamplifiers in common use is the fact that eiciency of these de- 'curve Ein Fig. CL.

be carefully and critically adjusted for every' vices is usually low.Unless the transformersl which are used in such equipment are of low Yresistance the degree of amplification must of necessity below. Theresistance of such a device is not limited to the conductor whichconstitutes its windings, but is often due, in a major Way, to losses inthe magnetic or dielectric material of its structure. lVhatever thelosses and hence the resistance may be, its eil'ect is the same, namely,to limit the amplification that can be secured through the use ofthedevice. i

ln Figu 2 l have illustrated the construction of radio frequencytransformer by which l secure the advantages herein set forth andparticularly shown by the characteristic The turns of wire com` prisingthe transformer 2 have been shown in greatly exaggerated size in all o'ie views yin order to clearly bring out the principle of my invention,and is will be understood that the transformer Winding comprises finewire turns Where the turns are represente large sise conductorse ein aircore is for ned hy winding the turns upon insulated. in 12. The primaryirincli begins as indicat ed reference character 8. The secondarywinding commences as indicated by reference characccr i0., P1he twinconductor isjwound upon the form 1:2., the turns 1 111 i or tie pinna-rywinding seing indicated section by cross-hatching slanting to the rigwhile theturns of the secondary winding are ywherein the coil supportingmember 12 is mounted upon core member within the closed core 14. y

In Fig. 4 the transformer Winding is illustrated disposedv on insulatingmember 12- forming an envelope for an iron core 16.

AThe turns of the primary Winding are Wound closely adjacent to theturns of the secondary winding and are parallel throughout the entirelength of the Winding. The turns are separated by the dielectric formedby the insulation enveloping each of the conductors. u,

The transformer may be suitably mounted as illustrated in Fig. 5 Withinan insulated cylindrical casing 17, bearing posts 1&-19- -21 on theexterior of the casing. The

primary winding beginning at 8 is connectedv interiorly of the case withpost 18 and at the end 9 the primary winding is connected within thecase with post 19. The secondary Winding 710 -is connected inside of thecasing with binding post 20 while the end of the secondary Winding 11connects inside of the case with' binding post 21. This arrangementpermits external connections to be made between the binding posts andthe electron tube circuits.

ln the operation of an electron tube ainplifier employing my invention,the power' is transferred from tube 3 of l to tube -l by means of thei'iiagnetic flux which interlinlrs the two windings of the transformer.

lillliere these two windings and their associated capacity which, forthe most part resides in the tube, are so chosen that they are tuned tothe saine wavelength as those shown in Fig. Q, that is, the primary ofthe transformer and tiie output capacity of the tube are tuned to thesaine wavelength as are the secondary winding and the input capacity ofthe tube and the power is transferred onli7 at the frequency at whichthey are timed. lf the resistance of the windings were kept very low itwould be found that the band over which the transformer could bedepended upon to give amplification would he even narrower than are thetransformers shown, and that the transformer would be so very unstableas to be entirely unusable. 7-lher-e are two methods by which this bandmay be broadened; one or them consists in inserting resistance in thetransformer winding or its associated material and thereby broadeningthe band of operation. This, of course, results in a reduction in thedegree of amplification in order to gain breadth of band, and results insuch amplification characteristics as are shown by curves A, B, and D in6. The other method is by increasing the coupling between tlie windingsas is secured with my transformer. lThis is accomplished by placing4 thewindings in the closest proximity to one another and results in abroadening` of the band without any sacrice in the degree ofamplification and with a degree of stability that cannot be secured byany other means. it is to be observed that this same result cannot be accomplished by the expedient of merely placing the windings of thetransformers of the prior and usual construction in close prox in iity.This would result in an increase of coupling, of course, but it wouldalso result in bringing into being much dielectric flux and greatdielectric loss with a consequent reduction of the degree ofamplification. ln the transformer construction of the present inventionthis increased coupling'is secured without increased dielectric loss bythe fact -that while the conductors of the two windings are extremelyclose to one another those parts of the conductors that are most closelyadjacent are always at the saine potential and therefore no dielectricflux exists and hence no loss. lt is essential for the successfuloperation of the transformer of my invention that the conductors be laidon parallel and that they be closely adjacent, and that they be closelyand permanently fixed relative to one another so that no dielectric lossas above described may be brought into being, for such loss will befatal to the operation'of the device. To this end it is found advisableto impregnato the entire device in wax or varnish. 'lliis cannot be donein prior constructions, since the dielectric field that alwaysaccompanies these prior types of construction would result in tremendouslosses.

By reason of this arrangement of the windings the rcactance gradientsalong all portions of the two conductors closely adjacent to one anothermust be substantially equal. 'llie currents in closelyadjaccnt portionsof the conductors are substantially equal in magnitude.

The transformer is particularly effective for quantity production sinceby its consti-uc tion all its electrical characteristics may be easilyreproduced. Since its inductance depends only on the size of conductor,number of turns, and the diameter of the forni` the coupling dependsonly on the position of 'the windings relative to one another, and henceonly upon the insulation thickness; and since coupling capacity iseliminated by the type of winding, it is found quite possible to buildthese devices by using only ordinary care with resultant variations'inthe constants in the transformers of a degree considerably less than itis possible to secure in the manufacture of the associated equipment ofelectron tube amplifiers such as the electron tubes per se.

In the claims hereinafter following l have used the term inductanceelement as enibracing the two windings parallel side by sidesubstantially throughout their length.

While l have described the transformer of this invention with particularreference to' radio frequency currents, it is to be understood that myconstruction is applicable to audio frequencies and that no limitationsare intended other than are imposed by the scope of the appended claims.

Having thus described my invention, what l claim and desire to secure byLetters Pah.

ent of the United States is:

l. An amplification system comprising in combination a plurality ofelectron tubes each having a heated cathode, an anode and a grid, inputcircuits including said grid and cathode of each tube, output circuitsincluding said anode and cathode of each tube, and coupling meansbetween the output circuit of one tube and the input circuit of anothertube comprising conductors connected in the respective circuits andfixed immediately adjacent and parallel side by side to one anotherthroughout the entire length thereof in such manner that the reactancegradients along all portions of the two conductors are substantiallyequal.

Q. An amplification system comprising in combination a plurality ofelectron tubes each lil having a cathode, an anode and a grid, inputcircuits including said grid and cathode, output circuits including saidanode and cathode, and coupling means between the outputcircuit of onetube and the input circuit of another tube comprising conductorsconnected in the respective circuits and wound u on a core, saidconductors being located adjacent put circuits including said anode andcathode,

` located immediately adjacent the conductor` and coupling means betweenthe output circuit of one tube` and the in ut circuit of another tubecomprising con uctors connected in the respective circuits and woundupon an iron core, the conductor in one circuit being in the othercircuit and insulation material for spacing said conductors parallelside by side throughout the length thereof, the potential of thoseportions of the conductors which are closely adjacent beingsubstantially equal 'for preventin dielectric `,flux therebetween.

4. VAn amp ification system comprising in combination a. plurality ofelectron tubes each lhaving a cathode, an anode and a grid, inputcircuits includin said grid and cathode output circuits inclu ing saidanode and cathode, andl coupling ineansvbetween the output circuit ofone tube and the input circuit of another tube comprising conductorsconnected in the respective circuits, the conductors being wound upon acore, the turns of one conductor being located alternately between theturns of said other conductor and immediately beside said conductor,whereby the reactaiice gradient along all portions of the conductorsissubstantially equal..

5. In an ampliication system a plurality of electron tubes each having aheated cathode, an anode and a grid, input circuits including said gridand cathode, output circuits including said anode and cathode andcoupling means between the output circuit of one tube and the inputcircuit of a succeeding tube, said means consisting of a twin conductorwound upon itself with one of the conductors connected in said inputcircuit and` the other of said conductors connected in said outputcircuit.

6. ln an electrical system, a grid, a plate, an inductance elementcomprising two windings wound parallel side by side throughout theirlength, the coefficient of coupling of said windings being substantialunity, a circuit including said grid and inductance element, Va circuitincluding said plate and' linductance element, adjacent points along therespective windings being at vtheVsa-me potential, the potentialgradient along any given portion of one winding being the same as thepotential gradient alon a corresponding portion of said other win ing.

LAWRENCE C. F. HORLE.

